Federal prosecutors in Michigan were working with an investigative team that included the FBI, the US Postal Inspection Service, the US Environmental Protection Agency’s Office of Inspector General, and the EPA’s Criminal Investigation Division, a spokeswoman for the US Attorney’s Office in Detroit said.

A Federal Bureau of Investigation spokeswoman said the agency was determining if federal laws were broken, but declined further comment. Also on Tuesday, EPA Administrator Gina McCarthy was meeting with officials and community leaders in Flint.

The city, about 60 miles northwest of Detroit, was under the control of a state-appointed emergency manager when it switched the source of its tap water from Detroit’s system to the Flint River in April 2014.

Flint switched back last October after tests found high levels of lead in blood samples taken from children. The more corrosive water from the river leached more lead from the city pipes than Detroit water did. Lead is a toxic agent that can damage the tissues of the nervous system.

Michigan Governor Rick Snyder, who extended a state of emergency in Flint until April 14, has repeatedly apologized for the state’s poor handling of the matter.

“It’s important to look at missteps at all three levels of government — local, state and federal — so such a crisis doesn’t occur again,” said Dave Murray, a spokesman for Snyder.

Last week, Michigan Attorney General Bill Schuette named a special prosecutor and investigator to look into possible crimes stemming from the matter.

APPeter Henning, a law professor at Wayne State University in Detroit and former federal prosecutor, said it would be a challenge to bring criminal charges, though Michigan state law may provide more options.

AP“We know this is a disaster, we know bad decisions were made, but there is this feeling that it has to have been more than just stupidity,” he said.

Henning cited Michigan’s misconduct in office law and neglect of duty misdemeanor offense.

In Washington, Senators Gary Peters and Debbie Stabenow, Democrats from Michigan, pushed for $600 million in aid, mostly in federal funds, to help Flint replace pipes and provide health care.

Meanwhile, Republican Senator James Inhofe, who chairs an environmental committee, said an agreement to help Flint was close and would be a combination of revolving funds and other aid he did not detail.

Senator John Cornyn, the second-ranking Republican, said any aid to Flint must not add to US budget deficits for “what is a local and state problem.”

The U.S. House Oversight and Government Reform Committee will hold a hearing on the Flint crisis on Wednesday and has invited the EPA’s acting deputy assistant administrator in its Office of Water to testify, as well as Keith Creagh, the new director of the Michigan Department of Environmental Quality. The previous director resigned in December in the wake of a critical report about the water.

The committee also invited Darnell Earley, the former Flint emergency manager, but he declined to testify. Earley, currently the Detroit Public Schools emergency manager, will step down from that position on Feb. 29.